The present invention relates to an automatic music or song selecting device for automatically selecting any arbitray music or song of two or more recorded on one side of a recording disc. More particularly, the invention relates to an intermusic or intersong detecting circuit for detecting the intermusic or intersong interval between adjacent songs by processing a signal from an intersong sensor for the automatic music or song selecting device.
In a conventional automatic music or song selecting device, a pickup cartridge incorporates an intersong detector having a light source and a photodetector and which is mounted in the vicinity of the tip of the stylus of the cartridge. When the pickup cartridge thus constructed is positioned adjacent the surface of the recording disc, the light emitted from the light source and reflected from the surface of the recording disc is detected by the photodetector. The intersong sensor detects the space or interval between adjacent songs on the disc on the basis of variations in the light reflected from the recording disc and accordingly produces an output signal varying in magnitude in accordance with the variations in the reflected light.
Such an automatic music selecting device is desirably capable not only of selecting one of a plurality of songs recorded on the recording disc, but also should be capable of selecting a plurality of sequential songs designated externally. In such a case, the automatic music selecting device must detect subsequent intersong intervals while playing another song. In case, for example, that the second and fifth songs are designated, the intersong sensor is in a leading-in state over the recording disc until the sensor arrives at the intersong interval between the first and the second songs and until the sensor is introduced into the intersong interval between the fourth and the fifth songs upon completion of playing of the second song on the disc. In this state, the intersong sensor must move at a considerably high speed together with the pickup cartridge. The intersong sensor, on the other hand, is in a playing or reproducing state while the cartridge is playing the second song and while the cartridge is playing the fifth song. In this case, the intersong sensor moves at slower speed together with the pickup cartridge than that during the leading-in time.
As a consequence, the signal waveform produced from the intersong sensor is different between the leading-in time and the reproducing time. Accordingly, the output signal itself from the intermusic sensor cannot be utilized directly as an intersong detection signal for controlling the automatic song selecting device.
To correct this problem, the conventional automatic music selecting device employed an intersong detecting circuit has employed a BPF (band-pass filter) the time constant of which is switched between the leading-in time and the reproducing time of the recording disc. The output signal from the intersong sensor is thus processed by the BPF for detection.
Since such a conventional intersong detecting circuit, however, must employ a BPF with a very large time constant for the reproducing time, a long time delay is involved, and accordingly typically more than several tens of seconds are required until the detecting circuit returns to the normal state after it detects an intersong interval.
Further, if there is an irregularity in the reflectivity of the surface of the recording disc or if there are different reflectivities in recording discs, such as between a black recording disc and a red recording disc, the conventional intersong sensor (as disclosed in Japanese Published Patent Application No. 43-5249, published 1968 cannot accurately detect intersong intervals between adjacent songs on recording discs.